This invention relates to a method of setting a wire electrode vertical for a wire cut electric discharge machine, and a device for practicing the method.
FIG. 1 is an explanatory diagram for a description of a conventional method of setting a wire electrode vertical for a wire cut electric discharge machine. In FIG. 1, reference numeral 1 designates a wire electrode; 2, a wire electrode supply reel; 3, a wire electrode take-up reel; 4, a lower guide roller; 5, an upper guide roller; 6, a lower wire guide; and 7, an upper wire guide. The wire electrode 1 is supplied, at a predetermined speed, from the wire electrode supply reel 1 through the lower guide roller 4, the lower wire guide 6, the upper wire guide 7 and the upper wire guide roller 5 to the wire electrode take-up reel 3, so that it is wound on the latter 3. For instance in the case where the wire electrode 1 is a brass wire 0.2 mm in diameter, generally a tensile strength of 800 to 1500 g is applied to it.
Further in FIG. 1, reference numeral 8 designates a wire guide drive unit for allowing the upper wire guide to move two-dimensionally, in the directions of U-axis and V-axis in a horizontal plane. The drive unit 8 is used to taper a workpiece (not shown) as required.
The workpiece is fixedly held on a machining table 10 with suitable clamp means which is movable two-dimensionally in the directions of X-axis and Y-axis in a horizontal plane.
A wire electrode perpendicularity meter unit 12 is provided on the machining table 10. The meter unit 12 comprises: a body 14 secured to the machining table; and an upper contact member 15 and a lower contact member 16 which are coupled to the body 14 in such a manner that the contact member 15 is positioned above the contact member 16 and they are in parallel with each other so that they maybe brought electrically into contact with the wire electrode 1. In addition, the wire electrode perpendicularity meter unit 12 is so designed that the line connecting an upper contact 151 and a lower contact 161 secured respectively to the ends of the upper contact member 15 and the lower contact member 16 is perpendicular to the machining table 10.
The contact signals of the upper contact 151 and the lower contact 161 with the wire electrode 1 are applied, respectively as an upper contact signal 20 and a lower contact signal 21, to a numerical control unit 18. The numerical control unit 18 applies an X-axis drive signal 22 and a Y-axis drive signal 23 respectively to an X-axis drive motor (not shown) and a Y-axis drive motor (not shown) which are provided for the machining table 10, and applies a U-axis drive signal 24 and a V axis drive signal 25 respectively to a U-axis drive motor (not shown) and a V-axis drive motor (not shown) provided for the wire guide drive unit.
The conventional method of setting a wire electrode vertical for a wire cut electric discharge machine will be described with reference to FIG. 2.
FIG. 2 shows a procedure of setting a wire electrode vertical in the direction of X-axis. The following description may be equally applied to the procedure of setting a wire electrode vertical in the direction of Y-axis.
In the case where the upper wire guide 7 is displaced to the right along the U-axis as shown in FIG. 1, the wire electrode 1 is not vertical as shown in FIG. 2(a). That is, the wire electrode 1 is inclined in the direction of U-axis, and both the upper and lower contacts 151 and 161 are off the wire electrode 1.
Therefore, the machining table 10 is moved forth in the direction of X-axis so that the lower contact 161 is brought into contact with the wire electrode. In this operation, the lower contact signal 21 is applied to the numerical control unit 18. Accordingly, simultaneously when the lower contact is brought into contact with the wire electrode, the machining table 10 is stopped. Then, the lower contact 161 is slightly moved back until it is disconnected from the wire electrode, as shown in FIG. 2(b).
Thereafter, the upper wire guide 7 is moved, for instance 1 .mu.m, to the left along the U-axis as shown in FIG. 2(c) so that the wire electrode 1 is raised.
The machining table 10 is moved in the direction of X-axis again, and it is determined whether or not the upper contact 151 and the lower contact 161 have been brought into contact with the wire electrode at the same time; that is, it is detected whether or not the upper contact signal 20 and the lower contact signal 21 have been applied to the numerical control unit 18 at the same time. When it is determined that the upper and lower contacts have not been brought into contact with the wire electrode at the same time, the operation described with reference to FIG. 2(b) is carried out again, and then the operation described with reference to FIG. 2(c) is performed again.
When it is determined that the upper and lower contacts have been brought into contact with the wire electrode at the same time, the machining table, the wire electrode, etc. are positioned as shown in FIG. 2(d). However, for confirmation, the machining table 10 is moved a predetermined distance backwardly, and then moved forwardly to determine whether or not the upper and lower contacts are brought into contact with the wire electrode at the same time. If it is determined that the upper and lower contacts have not been brought into contact with the wire electrode at the same time, then the machining table is set back as shown in FIG. 2(b) again, and it is moved 1 .mu.m again so that the wire electrode is held vertical. This operation is carried out repeatedly until it is detected that both the upper and lower contacts have been brought into contact with the wire electrode. When it is detected that the upper and lower contacts have been brought into contact with the wire electrode, then the wire electrode, the upper and lower contacts, etc. are positioned as shown in FIG. 2(e). Thus, the operation of setting the wire electrode 1 vertical has been accomplished.
In the case where the wire electrode 1 is inclined to the left of U-axis, the above-described method is equally employed to hold the wire electrode 1 vertical with the exception that, in this case, the upper contact 151 is firstly brought into contact with the wire electrode 1.
As is apparent from above description, the conventional method of setting a wire electrode vertical for a wire cut electric discharge machine is intricate and troublesome in practice. In order to determine whether or not the upper and lower contacts 151 and 161 have been brought into contact with the wire electrode at the same time, it is necessary to perform the contact ascertaining operation; that is, it is determined that the wire electrode is held vertical only when the upper and lower contacts are brought into contact with the wire electrode successively twice. Therefore, for instance when the wire electrode 1 is vibrated for some reason (it is liable to be vibrated), the phenomenon that the upper and lower contacts are brought into contact with the wire electrode successively twice may not occur. In this case, the wire raising operation is automatically carried out; that is, it may be performed more times than required, with the result that it takes a relatively long time to set the wire electrode vertical. If the wire electrode is being vibrated, the upper and lower contacts may be brought into contact with the wire electrode at the same time successively twice although the wire electrode is not held vertical yet. In this case, the wire electrode may not be sufficient in perpendicularity.
In order to eliminate the above-described difficulties accompanying the conventional method, for instance Japanese Patent Application (OPI) No. 61420/1982 has disclosed the following method (the term "OPI" as used herein means an "unexamined published application"): The upper and lower contacts are so designed as to be moved with spindles such as those of micrometers. The movements of the upper and lower contacts to the wire electrode are measured, and the amount of correction in position of the upper wire guide is calculated according to the movements thus measured, and the upper wire guide is moved according to the amount of correction thus calculated, to set the wire electrode vertical. However, it should be noted that the conventional method is held under the condition that the wire electrode is not vibrated. In addition, in the conventional method, the operation is manual. Hence, the conventional method is not suitable for the continuous operation or unmanned operation of an electric discharge machine.